Hydrocarbon liquid, more particularly oil, in many instances can be recovered from a subterranean formation through a well penetrating the formation by utilizing the natural energy within the formation. However, as the natural energy within the formation declines, or where the natural energy originally is insufficient to effect recovery of the hydrocarbon liquid, recovery methods involving addition of extrinsic energy to the formation can be employed. One of these methods, called the in situ combustion method, involves supplying a combustion-supporting gas (i.e., air or oxygen) to the formation and effecting combustion in place within the formation of a portion of the hydrocarbon liquid or of a carbonaceous residue formed from a portion of the hydrocarbon liquid. Downhole heaters and burners may be used for effecting such combustion. A combustion front migrates through the formation. The heat produced by the combustion reduces the viscosity of the hydrocarbon liquid ahead of the front and effects recovery of a greater portion of the hydrocarbon liquid within the formation than would be obtained in the absence of the combustion method. Such in situ combustion method is disclosed in U.S. Pat. Nos. 2,670,047 (Mayes, et al.); 3,379,248 (Strange); 3,399,721 (Strange); and 3,470,954 (Hartley).